mkvmuxer: remove unused timecode_scale variable
mkvmuxer: remove unused timecode_scale variable

unused in WriteFramesAll() / WriteFramesLessThan() since:
d6d04ac mkvmuxer: use generic Cluster::AddFrame

Change-Id: I2089dc24b6a942f342b278b46271c6144cf8351e

webmproject/libwebm,zofuthan/libwebm,webmproject/libwebm,felipebetancur/libwebm,webmproject/libwebm,zofuthan/libwebm,felipebetancur/libwebm